The present invention relates generally to noise cancellation and in particular to a noise cancellation circuit effective in suppressing noise component in the presence of peak-to-peak variations of the signal component. The noise cancellation circuit of the invention is particularly effective in suppressing noise in a composite video signal of television receivers.
A prior art noise cancellation circuit which has been proposed heretofore for television receivers operates on a signal derived from comparison of the instantaneous value of a composite signal with a threshold level. However, the average picture level (APL) of the composite signal may vary from instant to instant so that the peak level of the synchronization signal contained in the composite signal varies accordingly. Because of the variation of APL, the prior noise cancellation is not satisfactory.